Scissors lift mechanisms in general are known to the art. The principal purpose of such mechanisms is to provide a safe and efficient means for supporting a working platform at any desired elevation. The scissors lift mechanisms of the prior art are predicated on the well-known "lazy tong" principle, and each comprises a pair of vertically extensible scissors linkages mounted on a frame in laterally spaced, parallel relationship, and a working platform mounted on top of the linkages.
Each of the scissors linkages of the prior art lift mechanisms comprise pairs of arms pivotally connected to one another at their ends and at their centers. The lowermost pairs of arms of the linkages are pivotally mounted at one end to the frame, and they are slidably mounted on the frame at their other end. It is usual in the prior art scissors lift mechanisms to provide an hydraulic drive cylinder mechanism which is pivotally mounted to the frame, and which is coupled to a cross-bar extending between the lowermost pairs of arms of the linkages. The hydraulic lift mechanism serves to turn the arms of the lowermost pair about their pivotal axis to extend or retract the linkages and thereby to raise or lower the platform.
A disadvantage in the prior art hydraulic drive is the fact that as the lift mechanism is initially elevated from its lowermost position, the hydraulic cylinder/piston unit of the prior art hydraulic mechanism is positioned almost horizontal, and it must exert an excessively high trust on the mechanism to turn the lowermost arms and to start the vertical extension of the linkages.
Then, as the prior art lift is extended more and more in a vertical direction, the hydraulic lift unit pivots to an upright position, and it requires less and less thrust to move the load. This results in the need for an excessively large hydraulic lift unit in the prior art scissors lift in order to be effective to move the linkages from their retracted to their fully extended position, and it often leads to the requirement for auxiliary hydraulic lift mechanisms, as described above.
The improved construction of the present invention includes an hydraulic cylinder/lift unit which is mounted in an essentially fixed angular position such that the load vector is essentially aligned with the vertical axis of the unit, so that the thrust exerted by the unit is essentially in the direction of the load. Moreover, the hydraulic cylinder/lift unit in the mechanism of the invention is mounted such that the thrust exerted by it remains essentially invariable to move the load through all positions of the linkages. This results in minimizing the required capacity of the hydraulic lift unit without in any way detracting from the efficiency and safety of the unit, and it results in a more economical lift which is capable of movement from a fully compact position to a fully extended position in a simple, economical and efficient manner by means of an hydraulic unit having a fraction of the capacity required in the prior art scissors lift. Saddle mechanisms pivotally secure the upper and lower ends of the hydraulic lift unit in such manner that these units remain in essentially vertical positions.
Specifically, the invention provides a lift in which the hydraulic mechanism is capable of performing a desired function with less thrust and lower capacity requirements than the prior art mechanism, and on a more economical and safer basis.